The invention relates to a method for allocating a spatial radio resource in a communication system, and more particularly, to a method for allocating radio beams to specific users that have poor communication conditions.
Conventionally, radio resource managements in wireless communications manage radio resources in time and frequency domains. With the development of adaptive antenna systems (AAS), utilization of spatial radio resources is becoming more and more realizable, and managing the spatial radio resources is therefore increasingly important. For example, the standards of IEEE 802.16 family adopt AAS as an option to enhance cell capacity and coverage. The feature of AAS is its ability to reduce interference by steering the beam to a specific user. As a result the signal-to-interference-and-noise ratio (SINR) could be enhanced.
With a more advanced application of AAS, spatial division multiple access (SDMA), multiple beams can support multiple users at the same time. FIG. 1 is an illustration of a wireless communication system adopting SDMA. In a cell C1, a base station BS1 forms and allocates beams B1, B2, and B3 to mobile stations MS1, MS2, and MS3, respectively. Since the beams B1, B2, and B3 do not interfere with each other, the mobile station MS1, MS2, and MS3 can access the radio resource at the same time and frequency in the cell C1. In this way, the spectral efficiency of the wireless communication system is high, and the cell capacity can be significantly improved. In addition, interference suppression and SINR enhancement can be achieved. Furthermore, the frequency reuse factor, which is a well known method of reducing the interference with the tradeoff of the band width efficiency, can be increased. Since the main purpose of applying AAS is to suppress the interference, the interference level might be decreased by beam-forming under the same frequency reuse factor.
Usually, SDMA is combined with other multiple access schemes such as time division multiple access (TDMA) or orthogonal frequency division multiple access (OFDMA). Some scheduling algorithms for managing the radio resources have been proposed, e.g. the spatial grouping algorithm and the SDMA/TDMA scheduling algorithm. The conventional scheduling algorithms, however, fail to support poor quality users in the communication system with beam-forming, and thereby, quality of service (QoS) of the communication system cannot be guaranteed and improved.